1. Field of the Invention
This invention relates to a steering wheel the hand wheel part of which is made of injection molded foam of thermoplastic synthetic resin. This steering wheel is intended mainly for use in an automobile.
2. Description of the Prior Art
The desirability of the appearance of steering wheels of the type described above in the market has been finding growing recognition because these steering wheels promise improvement in producibility (quantity production), reduction in production cost, and decrease of weight. Various inventions have been proposed which are directed to steering wheels made of integral skin type (solid surface) injection molded foam of flexible PVC. In the production of such steering wheels, PVC materials of special formulations (ordinary PVC materials are liable to produce flow marks) must be used and, at the same time, the molding conditions such as temperatures of materials and metal dies and periods of die closure must be rigidly controlled in order that the flexible PVC materials may produce flawless solid surfaces by being foamed at prescribed expansion ratios (1.1 to 1.8 times the original volume). These rigid conditions of material formlation and foaming operation have resulted in increased material cost and decreased producibility.